After unwrapping, I kept it for more than a year before I started using it. Managed to finish it within a few months as there are only 52 pages.

The Delta series has the heavyweight 270gsm cold press watercolour paper, available in hardcover and wirebound. There's no mention of how much cotton content there is though. The paper is off-white.

The hardcover version is very well constructed and durable. Pages are stitched together and can open flat.

For mine, the part where it's glued to the spine of the pages have detached from the paper but the binding is still good and holding the pages together well. Just that for some pages, the gutter has become slightly larger.

The Delta series are currently only available in portrait orientation, and there's a square format only for the wirebound.

270gsm paper is thick and works well with watercolour. It's not as absorbent compared to cotton watercolour paper so be aware of not using too much water or it will be difficult to control.

The paper is almost like cardboard and doesn't warp even with heavy washes.

Since the paper is off white and slightly creamy, it does make the artworks look a bit warmer. Stillman & Birn does have natural white pages and those are from the Beta series which are also 270gsm.

I'm started to hate page gutters.

Here's a granulation test with QoR watercolours.

After you scan the drawings, adjust the levels, you can remove the warm bias and the colours will turn out quite nice. I like the granulation in the sky. That's Daniel Smith watercolours.

The coldpress surface texture is quite smooth but not like hotpress smooth. You can use pens easily without fearing that the tip will going into the crevices of textured surface.

Here I used watercolours and black brush pen.

I only drew a few sketches that were coloured with coloured pencils. I said early that the paper is quite smooth but it's also quite toothy when it comes to coloured pencil application. You'll get lots of white showing through.

After storing the sketchbook for more than a year without drawing, I see that some spots have appeared. I thought they were mould but my friend said they are oxidation spots because the paper isn't truly acid-free due to the inconsistent sizing. I've no idea what they are.

Conclusion

It's a well constructed and durable sketchbook good for mixed media and watercolours. I would love to see Stillman and Birn produce landscape oriented sketchbooks as well. So far, I know only their Alpha series have the landscapes.

Personally, I'm not a big fan of off-white paper when it comes to using watercolours. I prefer the Beta series for the white paper.

Overall, it's a great performing sketchbook for those who want quality. I don't have complaints except for the mysterious spots.

Does this sketchbook have double-sided pages or are the surface textures consistent on all the pages? Like, my Strathmore sketchbook has a cold press texture on one side and a hot press texture on the other.